LONDON – One star dimmed and another one exploded like a supernova in the semifinals of women’s boxing on Wednesday.

When American CoverGirl Marlen Esparza lost her flyweight semifinal to the three-time world champion Ren Cancan of China, 10:8, she ended an 11-year career that included six national titles and a world championship bronze medal. Although Esparza will earn an Olympic bronze medal for reaching the semis of the 48-51kg weight class in London, backstage, the disappointment eventually rolled out of the corners of her eyes and merged into the sweat rivulets streaming down her face.

“I’m my harshest critic,” she said, calmly wiping it all away with her ever-present stars-and-stripes bandana.

Esparza's bronze is the first ever medal for the United States in women's boxing, which made its Olympic debut earlier this week.

About an hour after Esparza’s loss, however, her 17-year-old teammate Claressa Shields of Flint, Michigan routed Marina Volnova of Kazakhstan in the middleweight semifinal, 29:15, with speed, flair, and powerful combinations that twice resulted in standing eight counts for Volnova.

As a result, Shields will fight again and may just bring the U.S. its first boxing gold medal since 2004, in the women’s middleweight (69-75kg) final on Thursday.

“When Errol [Spence] lost last night, I felt kind of heavy,” she said of the last American in the men’s draw, at 69kg. “Then it was just me and Marlen. Right now it’s all on me to get the gold medal.”

In the final, Shields will have to beat Nadezda Torlopova of Russia who captured a world championship bronze medal earlier this year at 75kg. Torlopova is nearly twice Shields’ age and has more international experience, but Shields has been boxing longer than Torlopova’s five years.

Also, Shields was far and away the better looking fighter on Wednesday.

“That was the performance I wanted everyone to see,” Shields said, and it was inspired by watching one of Sugar Ray Robinson and Jake LaMotta’s six fights between 1942 and 1951 on the eve of her bout. It is no coincidence, therefore, that Shields goes by the nickname “Baby Robinson.”

Meanwhile, Marlen Esparza had been one of the most marketed female boxers leading up to the Olympic debut of women’s boxing. Her final fight “was one of those chess matches,” said U.S. coach Charles Leverette.

Ren, a natural right-hander, fought southpaw for at least three of the four two-minute rounds, but Esparza had seen her do that before. “She did tactically what I thought she was going to do,” Esparza said. “I didn’t expect to win by a lot – one, two points at most. They [the judges] just didn’t see me for the last round.”

Esparza bounced around the taller, more relaxed Ren, and both displayed stellar defense and kept their hands relaxed and low, but Ren ultimately led after every round: 3:2, 7:4, 8:6 and finally, 10:8.

The two had also met in the quarterfinals of the 2012 world championships, where Ren prevailed, 16:8, leaving Esparza to finish fifth.

“I don’t think I’d do anything differently,” said Esparza, 23, said of her performance on Wednesday. “That’s the worst part. I did what I thought I was supposed to do.”

Esparza had long said the Olympics would be the end of her boxing career – foregoing the pro ranks to finish college – and the Houston native confirmed her plan in defeat.

“I wish it had ended on a better note, but that’s it for me right there,” she said.

Aimee Berg is a freelance contributor for TeamUSA.org. This story was not subject to the approval of the United States Olympic Committee or any National Governing Bodies.